Antennas for wireless voice and/or data communications typically include an array of radiating elements connected by one or more feed networks. For efficient transmission and reception of Radio Frequency (RF) signals, the dimensions of radiating elements are typically matched to the wavelength of the intended band of operation. Because the wavelength of the GSM 900 band (e.g., 880-960 MHz) is longer than the wavelength of the GSM 1800 band (e.g., 1710-1880 MHz), the radiating elements for one band are typically not used for the other band. Radiating elements may also be dimensioned for operation over wider bands, e.g., a low band of 698-960 MHz and a high band of 1710-2700 MHz. In this regard, dual band antennas have been developed which include different radiating elements for each of the two bands. See, for example, U.S. Pat. No. 6,295,028, U.S. Pat. No. 6,333,720, U.S. Pat. No. 7,238,101 and U.S. Pat. No. 7,405,710, the disclosures of which are incorporated by reference.
Additionally, base station antennas (BSA) with +/−45 degree slant polarizations are widely used for wireless communications. Two polarizations are used to overcome of multipath fading by polarization diversity reception. The vast majority of BSA have +/−45 degree slant polarizations. Examples of prior art can be crossed dipole antenna element U.S. Pat. No. 7,053,852, or dipole square (“box dipole”), U.S. Pat. No. 6,339,407 or U.S. Pat. No. 6,313,809, having 4 to 8 dipole arms. Each of these patents are incorporated by reference. The +/−45 degree slant polarization is often desirable on multiband antennas.
In known multiband antennas, the radiating elements of the different bands of elements are combined on a single panel. See, e.g., U.S. Pat. No. 7,283,101, FIG. 12; U.S. Pat. No. 7,405,710, FIG. 1, FIG. 7. In these known dual-band antennas, the radiating elements are typically aligned along a single axis. This is done to minimize any increase in the width of the antenna when going from a single band to a dual band antenna. Low-band elements are the largest elements, and typically require the most physical space on a panel antenna.
While +/−45 degree slant polarization is often desired, there are difficulties with using known validating elements to make a compact ±45 degree polarized antenna. Known crossed dipole-type elements, for example, are known to have undesirable coupling with crossed-dipole elements of another band situated on the same antenna panel. This is due, at least in part, to the orientation of the dipoles at ±45 degree to the vertical axis of the panel antenna.
The radiating elements may be spaced further apart to reduce coupling, but this would increase the size of the multiband antenna and produce grating lobes. An increase in panel antenna size may have several undesirable drawbacks. For example, a wider antenna may not fit in an existing location or, if it may physically be mounted to an existing tower, the tower may not have been designed to accommodate the extra wind loading of a wider antenna. Also, zoning regulations can prevent of using bigger antennas in some areas.
An object of the present invention is to create more compact +/−45 degree polarized antenna. Another object is to reduce the cost of base station antennas. Size and cost reduction of base station antennas (BSA) is vital for wireless communication systems.